Macimorelin vs MK-677 (Ibutamoren) — Peptide Comparison

Macimorelin vs MK-677 (Ibutamoren) — Peptide Comparison Macimorelin vs MK-677 (Ibutamoren) — compare dosing, benefits, safety profiles, side effects, and how they stack. See which peptide is right for you. At a Glance Dose Range Macimorelin 25–60 mg MK-677 (Ibutamoren) 10–25 mg Frequency As needed Once daily Administration Oral (reconstituted solution) Oral (capsule or liquid) Cycle Length 4-6 weeks 8-12 weeks Onset Speed Rapid (hours to days) Moderate (1-2 weeks) Evidence Level Strong human trials (Phase 3 or FDA approved) Moderate human trials (Phase 1-2) Efficacy Diagnostic Accuracy Safety & Tolerability Convenience & Patient Experience Muscle and body composition Recovery and athletic performance Sleep quality and metabolic health Technical Data Molecular Formula C26H30N6O3 Molecular Weight 474.6 g/mol Half-Life 4.1 hours Bioavailability Oral; food decreases Cmax and AUC by approximately 50-55% — must be administered fasting CAS Number 381231-18-1 C27H36N4O5S 528.7 g/mol 4-6 hours (IGF-1 elevation persists ~24 hours) High oral bioavailability 159634-47-6 Protocols standard 0.5 mg/kg Single dose One-time diagnostic test FDA-label (Macrilen) single oral dose for diagnosing adult growth hormone deficiency. Granules (60 mg) are reconstituted in 120 mL water (0.5 mg/mL) and taken after an 8-hour fast; serum GH below 2.8 ng/mL across the 30/45/60/90-minute draws confirms deficiency [4]. starting 10 mg 2-4 weeks initial Lower entry dose used in practice to limit water retention and appetite surge before titrating up. 25 mg Studied up to 1-2 years 25 mg once-daily oral is the dose used in the randomized trial in healthy older adults; increased GH/IGF-1 and fat-free mass [1]. Most-studied dose [2]. Applications Diagnosis of Adult Growth Hormone Deficiency Macimorelin is FDA-approved specifically for diagnosing AGHD in adults. It replaces the insulin tolerance test (ITT) as a safer, more convenient, and equally accurate diagnostic option. Phase 3 trials showed 87% sensitivity and 96% specificity. Patients Intolerant or Contraindicated for ITT For patients who cannot safely undergo insulin tolerance testing due to cardiac risk, seizure history, or other contraindications, macimorelin offers an evidence-based non-invasive alternative. Clinical Confirmation Testing With 97% reproducibility on retesting, macimorelin can reliably confirm GH deficiency diagnoses and monitor therapeutic responses over time with excellent consistency. Older Adults (60+) Seeking Body Composition Improvements MK-677 was designed for aging populations. It restores GH and IGF-1 to youthful levels, increases lean mass, and improves physical function in people over 60. A 2-year clinical trial showed a 1.1 kg gain in fat-free mass with only modest fat gain—ideal for maintaining strength in older age. Athletes and Fitness Enthusiasts Wanting Recovery Support Oral dosing makes MK-677 convenient for athletes. It enhances muscle protein synthesis, speeds recovery after intense training, and supports lean mass building without the hassle of injections. People with Chronic Wasting or Protein Deficiency Clinical trials show MK-677 helps treat protein-energy wasting in kidney disease and other conditions. It stimulates appetite (a feature in these populations) and preserves muscle tissue—making it useful for those losing mass despite good nutrition. Safety Profile Common Dysgeusia (abnormal taste) Dizziness Headache Fatigue Nausea Increased Appetite Serious Cardiovascular events Increased appetite Mild water retention or edema Elevated fasting glucose Uncommon Joint or muscle pain Carpal tunnel syndrome or nerve compression symptoms Mild nausea or digestive upset Glucose dysregulation and diabetes risk Research Status FDA Status FDA approved for this use Safety Overview Macimorelin is well-tolerated with an excellent safety profile in clinical trials. No serious adverse events were reported in Phase 3 studies (n=154). Most side effects are mild and transient. QT prolongation of approximately 11 msec occurs but is generally not clinically significant. However, avoid combining with other QT-prolonging drugs. Contraindications xPatients with QT prolongation or QT/RR prolongation disorder xConcurrent use with drugs known to prolong QT interval xPatients with critical illness (acute medical or surgical illness) xKnown hypersensitivity to macimorelin or any components xPatients unable to fast or follow fasting requirements Research compound MK-677 has been studied in hundreds of humans over 2+ years and is generally well tolerated. Most side effects are mild and manageable, especially with lower starting doses. The lack of injection requirement makes it safer than injectable GH in terms of infection risk and sterility concerns. However, it is not FDA approved and should be viewed as a research compound. xUncontrolled diabetes or severe glucose dysregulation xActive cancer or high cancer risk requiring caution with IGF-1 elevation xPregnancy or breastfeeding Decision Guide Choose Macimorelin if... Diagnosing adult growth hormone deficiency (AGHD) Patients who cannot tolerate or are contraindicated for insulin tolerance test Clinical settings requiring convenient, repeatable hormone testing Healthcare providers seeking FDA-approved diagnostic alternatives Choose MK-677 (Ibutamoren) if... Building lean muscle mass and strength Improving overall body composition in aging adults Enhancing athletic recovery and performance Supporting metabolic health and fat loss